A fuel cell is a device that converts chemical energy of a fuel into electrical energy, typically by oxidizing the fuel. In general, a fuel cell includes an anode and a cathode fluid flow plate separated by an electrolyte. When fuel is supplied to the anode and oxidant is supplied to the cathode, the electrolyte electrochemically generates a useable electric current that is passed through an external load. The fuel typically supplied is hydrogen and the oxidant typically supplied is oxygen. In such cells, the electrolyte combines the oxygen and hydrogen to form water and to release electrons.
The anode and cathode fluid flow plates are made of an electrically conductive material, typically metal or compressed carbon, in various sizes and shapes. Fluid flow plates act as current collectors, provide paths for access of the fuels and oxidants to the cell, and provide a path for removal of waste products formed during operation of the cell. Additionally, the fluid flow plates include a fluid flow field of channels for directing fluids within the cell.
Fuel cells are classified into several types according to the electrolyte used to accommodate ion transfer during operation. Examples of electrolytes include aqueous potassium hydroxide, phosphoric acid, fused alkali carbonate, stabilized zirconium oxide, and solid polymers, e.g., a solid polymer ion exchange membrane.
Fuel cells usually are arranged as a multi-cell assembly or “stack.” In a multi-cell stack, multiple cells are connected together in series. The number and arrangement of single cells within a multi-cell assembly are adjusted to increase the overall power output of the fuel cell. Typically, the cells are connected in series with one side of a fluid flow plate acting as the anode for one cell and the other side of the fluid flow plate acting as the cathode for an adjacent cell.
Fluid flow plates also have holes therethrough for alignment and for formation of fluid manifolds some of which distribute fuel and oxidant to, and remove unused fuel and oxidant as well as product water from, the fluid flow fields of the plates. Other fluid manifolds circulate cooling fluid. Cooling mechanisms, such as cooling plates, may be installed within the stack between adjacent single cells to allow circulated cooling fluid to remove heat generated during fuel cell operation. Each layer in the stack is cooled to prevent overheating and to provide an optimum environment in which ions cross the electrolytes in each cell.
Pressurized cooling fluid, such as water, may be provided through a manifold to ensure that water reaches each cell in the stack and to provide proper cooling within that cell. However, the pressure in the manifold may be greater than necessary to cool each cell. Openings from the manifold to a water path within each cell are then desired to be smaller to ensure a proper pressure drop into each cell and therefore, a proper flow rate through each cell. However, smaller openings may be prone to blockage and such blockage may cause overheating that can damage a cell and a stack.
The conflicting requirements of small openings from the manifold to each cell and minimized blockages are typically satisfied by using long coils of tubing and flow splitters for each pair of cooling elements. This solution however, is costly in terms of both materials and labor.